Many mobile devices currently include a location-determining ability, usually based on a Satellite Positioning System (SPS), such as Global Positioning Satellite (GPS) technology. For mobile phones, a common location-determining technology is Assisted GPS (AGPS), where at least some of the data used for calculating position is supplied by an assistance server, rather than (or in addition to) directly from a satellite. For example, some mobile devices receive ephemeris data from assistance servers.
Ephemeris data provides precise orbital information for a given Space Vehicle (SV). In current GPS systems, for example, ephemeris data is usually considered reliable for a four-hour window, X−2 to X+2, where X is a time, usually an even hour. When an AGPS-enabled device initiates a positioning application, it requests information from the assistance server, including requesting ephemeris data for SVs that are visible and for some SVs which may be expected to become visible within a short (usually 4-hour) window.
The ephemeris data for most, or nearly all, space vehicles expires at or near an even hour time (e.g., two o'clock, four o'clock, etc.). Thus, even though a mobile device may have powered up or otherwise activated its location-based service at a time different from an even hour, the chances are high that the mobile device will request a refresh of the ephemeris data, for at least some space vehicles, at the next even hour. Within a given cell of a mobile communication network there will typically be multiple mobile devices operating, such that even hour times often see spikes in the numbers of refresh requests to assistance servers. When the spikes are large, mobile phone networks run a risk of providing poor performance to customers due to assistance server overloading. There is currently no technique available to effectively prevent refresh request spikes.